1. Field of the Invention
The present invention relates to a general purpose engine in which a case main body, which is a principal part of a crankcase, is integrally formed with a cylinder block, a crankshaft having a plurality of crank webs is rotatably supported via bearings in the case main body and a bearing support member mounted on the case main body, and a drive transmission wheel housed within the crankcase so as to transmit rotational power to a valve operating mechanism is fixedly provided on the crankshaft so as to be outside the crank web that, among the crank webs, is at one end in the axial direction.
2. Description of the Related Art
A general purpose engine in which a crankcase is formed from a case main body and a cover joined to the case main body, and the cover is used as a bearing support member, is already known from, for example, Japanese Patent Application Laid-open No. 2001-329910.
However, in this conventional arrangement, the cover (the bearing support member) is disposed outside a drive transmission wheel fixedly provided on a crankshaft so as to be outside a crank web that is at one end in the axial direction. Consequently, the distance between a crankpin and the cover is comparatively long, and thus the rigidity with which the crankshaft is supported is comparatively low. As a result of a load acting on the crankshaft in a direction perpendicular to the axial direction during a combustion stroke, etc., a comparatively large knocking sound is generated in a gap between the crankshaft and a bearing supported by the bearing support member.
In order to solve this problem, it is conceivable that the bearing support member, which is a separate member from the crankcase, is mounted on the case main body inside the cover, and the distance between the crankpin and the bearing support member is made comparatively short, to thereby enhance the rigidity with which the crankshaft is supported. However, when the interior of the crankcase is divided into two by means of the bearing support member, the amount of oil that can be held within the crankcase becomes small, leading to a possibility that the continuous operation time might be reduced. If an attempt is made to ensure a sufficient amount of oil, the dimensions of the crankcase, and consequently those of the general purpose engine become too large.